The Japanese language is said to have started writing in kanji (Chinese characters) in early 5th century. I complied ancient kanji materials, including those of even older kanjis which had been used isolated, into a data base, and made a chronological table. I believe these studies resulted it possible to get a general idea of how the description of the Japanese language was developed.Kun (Japanese way of reading kanji) is the most characteristic of Japanese usage of kanji.The earliest sure example of kun is found in the middle of 6th century. In early 6th century Confucianism and Buddhism which were introduced to Japan via Korea, accelerated kundoku (Japanized way of reading) of kanbun (Chinese writing) in Japan. I presume authentic kanbun has transformed into hentai-kanbun (Japanized kanbun) by the end of 6th century. under the influence of zoku-kanbun (vulgar ancient Korean Chinese writing) and frequent use of kun, then into the mixture of kanji and Manyoo-gana (Kana is the Japanese syllabary. Manyoo-gana is the first kana used in Manyoo-syu) , as a result of the effort to describe the phonetic system of the Japanese language as precise as possible. This is the prototype of the modern Japanese writing, which is consists of kanji and kana. Thus I could make it clear, how the Japanese writing style has developed and established.Going through these studies, I would like to publish this treatise translated into various languages to help the foreign researchers who are interested in the subject.